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C.G. Begley, R.L. Chalmers, M. Christensen; Within and Between Subject Repeatability of Tear Break Up Dynamics . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1955.
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The purpose of this pilot study is to determine the repeatability of the Tear Break Up Dynamics (TBUD) measurement over one week. A secondary purpose was to compare the repeatability of this measure to other standard clinical measures of tear stability, the TBUT.
Eight symptomatic subjects who had been diagnosed with dry eye received standard dry eye tests and 8 repeated measures of forced staring tear break up dynamics (FS–TBUD) at 2 sessions 1 week apart. TBUD measurements include the digitally analyzed total area of break up (AB), the Maximum Blink Interval (MBI) and the digitally analyzed first Tear Break Up Time (TBUT) at "run" times of 0, 15, 30 and 60 minutes. Inter– and intra–subject variability were calculated as the square root of the mean square error terms from a single factor (subject) ANOVA which partitions all experimental variability into either inter– or intra–subject variability.
The group mean and group SD were: TBUT=5.9 sec (6.3sec); AB=13.4% (10.4%); MBI=16.5 sec (14.5sec); AB/MBI=1.12%/sec (0.94%/sec). There was significant inter–subject variability, but no significant systematic differences due to visit or "run". Comparison of between and within subject variability (mean square error) for each measure was: TBUT = 11.2 sec vs 5.3 sec; AB = 21.2% vs 7.8%, MBI = 36.6 sec vs 8.2 sec and for AB/MBI was 2.0%/sec and 0.6%/sec (p<0.05 for all variables).
The signal to noise ratio for TBUT for the average of all subjects is high, more than a 1:1 ratio; within subject variability was slightly lower. The AB/MBI has better signal to noise ratio for within–subject comparisons than TBUT. Relative to TBUT, that yields information on only one point in time, the AB/MBI measure is a more stable measure of tear stability in this sample of untreated dry eye subjects. The lower amount of within–subject variability also points to the use of within–subject study design and analysis for dry eye treatment trials.
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